1. 1) S. V. Dubovetskii and G. I. Sergatskii: Automatic Welding, 33 (1980), 22.
2. 2) H. Carlslaw and J. C. Jeager: Conduction of Heat in Solids, 2nd edition, Chap. XIV, Oxford Univ. Press, (1959), p. 56.
3. 3) M. S. Bazaraa and C. M. Shetty: Nonlinear Programming, John Willy & Sons, (1979), p. 38.
4. 4) P. Wolfe: Economotrica, 27 (1959), 382.
5. 5) T. Ohji and K. Kondoh: J. Japan Welding Society, 8 (1990), 48.